Question on RPMs
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Junior User
Joined: Jan 2008
Posts: 60
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From: Chehalis, WA
Question on RPMs
Hi Guys and Gals,
I have been reading all the posts about MPG and stuff where people are keeping the RPMs at 2k and still doing about 70 MPH. I am keeping mine at 2k but am only going around 62 MPH (speedo says 65ish). I know my speedo is off by a couple, mile checked it and used a GPS. Is this a normal speed for 2k?
2001 F350 CC SRW, stock tires, 3.73 gearing, 6637 (let me know if you need more info)
Thanks
Dan
I have been reading all the posts about MPG and stuff where people are keeping the RPMs at 2k and still doing about 70 MPH. I am keeping mine at 2k but am only going around 62 MPH (speedo says 65ish). I know my speedo is off by a couple, mile checked it and used a GPS. Is this a normal speed for 2k?
2001 F350 CC SRW, stock tires, 3.73 gearing, 6637 (let me know if you need more info)
Thanks
Dan
Hook it, I'll pull it.
Joined: May 2007
Posts: 15,037
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From: Grand Lake, La.
Dan, If you have 4.10 gears, you are right on. That is what I get on mine, and I have 4.10 gears.
EDIT: I see you have 3.73 gears. Are you sure about this? That is what I get on my 4.10 gears.
EDIT: I see you have 3.73 gears. Are you sure about this? That is what I get on my 4.10 gears.
Post Fiend
Joined: Mar 2007
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From: Texas
You could also get pretty close by doing it the old fashioned way. Jack up the rear wheels, spin them 1 revolution and count the number of times the driveshaft turns.
Senior User
Joined: Nov 2006
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I have 3.73s & run dead on 70mph at 2k.
Crawl under your truck & see if there is a tag in the cover under 1 of the bolts & see what it says.
My guess is someone changed the gears to 4.10s best way to figure it out without getting into the diff is to mare the driveshaft & tires & spin the drive shaft (with the trany in N & front tires chalked) & see how many times it goes around compared to the tires.
Crawl under your truck & see if there is a tag in the cover under 1 of the bolts & see what it says.
My guess is someone changed the gears to 4.10s best way to figure it out without getting into the diff is to mare the driveshaft & tires & spin the drive shaft (with the trany in N & front tires chalked) & see how many times it goes around compared to the tires.
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From: Hampton, Maryland.
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Gone, but not forgotten
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From: Charlotte-Fairbanks-Bflo
I can improve on this idea a little, but it is nearly a 2 person job. Chalk marks BDC tire and BDC drive shaft. You turn the tire (the work part) and have your wife or whoever count the number of times the drive shaft turns. This is a really cool method if you're using something other than stock tires which can cause your final drive ratio to vary dramatically.
Gone, but not forgotten
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From: Charlotte-Fairbanks-Bflo
Just about the exact same thing for me with same setup, which is why I spend most of my time at 62-63 mph. Screw the tailgaters. They want me to drive faster as I would prefer to, let them meet me at the next truck stop, with their credit card.
Lead Driver
Joined: Jan 2007
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From: Kiowa CO
That's sounds right for me, stock rims and tires with a 3.73 rear diff gearing.
Thread Starter
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Junior User
Joined: Jan 2008
Posts: 60
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From: Chehalis, WA
Checked the tag on my diff. Here is what it says
S 409 H
L73 10 5 1B28
Guessing the L73 means the 3.73 gearing. I will have to borrow a jack to test manually.
Thanks again for the info.
edit: YAY! a sig!
S 409 H
L73 10 5 1B28
Guessing the L73 means the 3.73 gearing. I will have to borrow a jack to test manually.
Thanks again for the info.
edit: YAY! a sig!
